That's half the fun of eating spaghetti!

Everyone comes with characteristics that we like, those we tolerate, and a few things that are intolerable. OP, you have to decide if this is important to you - As is, don't count on being able to train BF into eating neatly. In the meantime avoid all foods with noodles... It's sad in a way, but not everyone gets the training as a child or young adult to avoid being a potential unappetizing embarrassment at mealtimes. And by the time they become an adult, they are sometimes unwilling or unable to change. Being a sloppy eater isn't in any sense the worst thing a person can be. And it's possible that they could learn to eat more properly if lovingly instructed - But that's not always the case.

Did he leave the mess? Or did he clean up after himself and you are complaining about nothing?